This invention relates to an improved dye penetrant composition and method for non-destructively testing materials to locate defects open to the surface, such as cracks, and is more particularly concerned with the provision of an extender which is compatible with the liquid vehicle of the dye penetrant, and is compatible with the metals or alloys, particularly titanium and nickel alloys, of which the objects being tested are comprised, as well as possessing other important characteristics such as low viscosity, low volatility, quick penetration into cracks and voids, and low toxicity.
In known penetrant inspection methods for rapid location and evaluation of surface flaws such as cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface of cracks or other voids in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions such as invisible fluorescigenous light, and the location of the surface cracks is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high sensitivity.
Volatile type solvents are commonly employed for extending or thinning dye penetrant inspection solutions or compositions. This is done chiefly for the purpose of lowering the viscosity of the penetrant in order to adapt it for application in spraying systems. Thus for example solvents such as kerosene, light fuel oils, light mineral oil, mineral thinner and methyl ethyl ketone, all highly volatile solvents, have heretofore been employed in prior art dye penetrants. See for example U.S. Pat. Nos. 2,806,959 and 3,429,826. Further, most dye penetrant solutions in practice generally require the use of a combination of solvents, including primary and secondary solvents, extender solvents and wetting agents.
Further, with the advent of new alloys employed in aircraft construction, such as titanium and nickel alloys, considerable effort has been made in selecting solvents which can be compatible with such alloys. Solvents compatible with these alloys generally are selected because of their unusually low chloride content and low sulfur content.
Accordingly, an object of the present invention is the provision of an improved dye penetrant composition containing an extender which has a number of unique advantages over extenders previously employed in dye penetrant compositions. A particular object of the invention is the provision of a novel dye penetrant composition containing an extender which is relatively inexpensive and which is compatible with certain dye penetrant composition vehicles and with certain alloys used in aircraft construction such as titanium and nickel alloys, and particularly affording a dye penetrant composition of low viscosity, low toxocity and which is substantially odorless. A further object is to provide procedure for dye penetrant inspection of objects, utilizing such dye penetrant composition.